How much did Euclid Tsakalotos have to do with Sinn Fein's change of tack on the welfare reform provisions of the Stormont House Agreement? Or Savvas Xiros?

Tsakalotos was the representative of the Greek ruling party Syriza who addressed the Sinn Fein ard fheis in Derry last Saturday. It's reported that he and leading Sinn Fein members afterwards talked late into the night - perhaps late enough for news of the occupation of Syriza's head office in Athens to come through.

About 50 members of an anarchist organisation had taken over the offices and dropped banners from the balconies calling for the closure of high-security prisons and the release of, in their definition, political prisoners.

They claimed Syriza had promised during the recent election campaign to release the prisoners, to repeal "anti-terror" laws and to close "Type C" prisons. But there was no sign of this happening, they complained.

Syriza's just-appointed official spokeswoman, Rania Svigou, told the Press: "I was inside my office giving my first official interview to a radio station. Then I heard banging and shouting. I finished the interview and went out to see what was happening and they told us to get out."

They did get out, but - strange as it might seem for a party of government - didn't call the police. Before coming to power, Syriza had been strongly critical of heavy-handed policing of protests - many organised by themselves.

The occupation ended peacefully, the anarchists saying that they had received assurances the prisons issue would be dealt with without further delay. A number of banners had expressed solidarity with prisoners who had gone on hunger strike against conditions designed, they claimed, for dangerous criminals rather than for political dissidents.

The occupation specifically highlighted the case of Savvas Xiros, an iconic figure on the Greek far-Left. He is said to have been the chief bomb-maker for an urban guerilla group, November 17th - named after the date of an uprising at Athens Polytechnic in 1973 against the military junta of Georgios Papadopoulus.

The rising was put down with considerable brutality. Scores were killed and hundreds imprisoned, many for years without trial.

November 17th hit back with sabotage, robberies and assassinations. However, time has passed and democracy rules again in Greece. Xiros is gravely ill - deaf and almost blind. Calls for his release from a life sentence on humanitarian grounds have been supported by human rights and liberal organisations.

Syriza may well feel trapped between its rock-solid promises of radical change and the hard realities of power. If it closes the "Type C" prisons and frees prisoners including Xiros, it risks denunciation for being soft on terrorism by countries whose goodwill it now needs.

On the other hand, a refusal to free the prisoners would be regarded by many of its most fervent supporters as shameful betrayal.

There are no parallel circumstances here. But Sinn Fein leaders will have appreciated better than most the difficulty of balancing requirements of the present with principles from the past.

Some within Syriza may be inching towards an ingenious way out of this impasse which could also have appeal for Sinn Fein. Referendum, anybody?

Even as delegates in the Millennium Forum were rising to acclaim Mr Tsakalotos, the Greek finance minister, Yanis Varoufakis, was telling the Italian newspaper Il Corriere della Sera that his government might call a referendum on the economic policies which the IMF, the ECB and the European Commission want to impose.

Not a referendum on membership of the Eurozone, he stressed, but only on the cuts being demanded of Greece.

The suggested reasoning is intriguing. If the people voted to reject the Troika's demands, Syriza could argue that Europe was faced with a choice between democracy and the rule of bankers and bureaucrats, and appeal for support across the Eurozone.

If, on the other hand, the people were to embrace the Troika's austerity package, Syriza could with some vestige of honour abandon its election pledges, in obedience to the democratic will of the masses.

Convoluted? No more convoluted than the situation in which Sinn Fein now finds itself with regard to the Stormont House Agreement and welfare reform.

Pushing for a referendum on the welfare provisions could offer the party a more plausible way out of its present predicament than continuing to insist that it hadn't understood the full implications of the agreement until struck by a blinding flash of light, just as Mr Tsakalotos waved goodbye and set off back to Athens.